On the Job

Steel I-Beam Rafter Pair

by
Dan Kolbert
In most stick-framed roofs, ceiling joists or collar ties
prevent the rafters from pushing out against the walls. With
cathedral ceilings — which have no joists or collar ties
— a structural ridge is necessary to support framing
members like rafters, hips, and valleys. The ridge is usually
carried by gables, walls, or posts.

But what do you do when there is nothing there to support one
end of the ridge?

Late last year, our company framed an addition that had a
cathedral ceiling and a roof with hip rafters. The main wall of
the house supported one end of the structural ridge, but
because of the hips, the other end stopped short of the
addition's exterior wall.

Luckily, the engineer on the project came up with an elegant
solution: a pair of steel I-beams welded together off-site in
the shape of two opposing rafters (1). We installed this
angle-shaped I-beam at the end of the ridge where the
king-common rafters would normally go, and had a plate
site-welded onto it to catch the one hip that carried a
significant load (2). The beam supports the ridge and hips
while still allowing for a cathedral ceiling (3).

Since the rafters were deeper than the I-beam, there was room
to create a thermal break by installing a small amount of rigid
insulation above and below the steel.

Rock-Breaking Tip

by David
Dobson

First, heat the rock with a torch.

Pour cold water over the rock where it's been
heated.

Hit the rock with a hammer where you want it to
split.

The broken rock.

Back when I was a young intern architect, one of the projects I
worked on was the renovation of a building on St. Thomas in the
Virgin Islands. The centuries-old structure — the house
where the French Impressionist painter Camille Pissarro was
born — had rubble walls up to 20 inches thick, and our
client wanted to cut niches in them for display cabinets.
Unfortunately, there was a large rock extending the entire
width of the wall, and the contractor could not figure out how
to cut or remove it without damaging surrounding areas.

When he came to our office with this dilemma, I suggested that
he split the stone by heating it with a torch, throwing
ice-cold water on it, and then hitting it with a hammer.

The contractor and I had already had some disagreements, so
when he heard this he looked at me as if I were crazy and said
there was no way it would work. But since he couldn't come up
with anything better, our boss told him to give my method a try
the following morning.

When we arrived on site, the contractor had his whole crew
assembled so that they could have a laugh when my method didn't
work. He heated up the rock with an acetylene torch and threw
water on it; then he looked at me and said, "See? Your idea
doesn't work."

"I also said that you need to hit it with a hammer," I
replied.

So he instructed a young laborer to hit the stone with a
hammer. After three hits, the contractor glanced at me and was
about to say something; on the fourth, the stone split right
along the back plane of the niche exactly where we wanted it
to.

It seemed best at the time to keep the source of the trick
— a filmstrip I saw in fifth grade — to myself. The
movie showed how workers built Stonehenge by heating the large
stones, throwing water on them, and hitting them with smaller
rocks.

David Dobson is an architect and licensed
general and glazing contractor in San Diego.

Ice Supports

by William
Dillon
Cool thinking saved the day recently when our design/build
firm hit a snag moving a 200-year-old house onto a new
foundation on Martha's Vineyard, Mass.

Ordinarily, we leave pockets in a foundation so that once the
structure is in place we can remove the beams we used to lift
and move it. But since this house was going on a structural
slab — with no basement or crawlspace — that
approach wasn't going to work.

Fortunately, house-mover Mike Reid had an ingenious solution:
He temporarily supported the building on blocks of ice while he
pulled out the beams. As they melted, the blocks lowered the
house about 1/8 inch per hour, giving him plenty of time to
remove the cribbing. We had to shade one of the blocks because
it melted faster than the others, but otherwise the plan worked
great.

This wasn't the first time Reid had used the technique. He told
us he once filled an elevator shaft with ice so that he could
lower a 10-ton piece of equipment in an elevator with a one-ton
capacity. A few days later, when the ice had melted, he pulled
the machine out of the elevator car and collected his
check.

William Dillon is a job supervisor with South
Mountain Co., an employee-owned design/build firm on Martha's
Vineyard, Mass.